In this paper, we perform CFD simulations by using FLUENT to analyze the flow uniformity in a chamber which is a main part of SCR system. Since the size of catalyst is extremely small compared to total size of the chamber, we employ an equivalent system which is a porous model is applied. The RMS (Root-Mean-Square,%) value of flow uniformity at the front section of the first catalyst is found to be 30.87% , and the total pressure drop between the inlet and outlet is found to be around 270Pa, which is lower than acceptable standard, 1kpa. In addition, we simulate three cases by changing position of the first catalyst. As a result, there is a difference between them within 3~5%. Finally, we investigate structural stability through FSI (Fluid-Solid-Interaction) analysis for existing model.